Oligonucleotides and their analogs have been developed for various uses in molecular biology, including use as probes, primers, linkers, adapters, and gene fragments. In a number of these applications, the oligonucleotides specifically hybridize to a target nucleic acid.
In certain instances, chemical modifications have been introduced into oligonucleotides to increase their usefulness in diagnostics, as research reagents and as therapeutic entities. Such modifications include those designed for a variety of purposes, for example: to increase binding to a target nucleic acid (i.e., increase their melting temperature, Tm), to assist in identification of the oligonucleotide or an oligonucleotide-target complex, to increase cell penetration, to stabilize against nucleases and other enzymes that degrade or interfere with the structure or activity of the oligonucleotide, to provide a mode of disruption (a terminating event) once sequence-specifically bound to a target, and to improve the pharmacokinetic properties of the oligonucleotide.